Publications

Saline aquifers, with their large connected areal extent, have the potential to store significant quantities of CO2 compared to depleted reservoirs. Saline aquifer pressures are usually close to virgin pressure as there is no hydrocarbon accumulation. Consequently, CO2 injection could raise pressures above the initial conditions of the aquifers, increasing leakage risks due to fault reactivation and fracturing of caprocks. Therefore, storable quantities are significantly influenced by the chosen scenario of regional aquifer size and connectivity, and assumptions about fault reactivation and fracturing of caprocks. Aquifer size controls how quickly pressure can dissipate while caprock competency determines the maximum allowable injection pressure; this paper concerns itself with injection pressure below the maximum allowable injection pressure, in which case small regional aquifers quickly pressure up, thereby limiting storable CO2 quantity. Connectivity matters because open boundaries that connect saline aquifers to much larger regional aquifers allow faster pressure dissipation, enabling faster injection while preserving caprock integrity.

In this paper, we share methods through which open boundaries can be modelled, and discuss the strengths and weaknesses of each. Given that scarce data availability for injection into isolated saline aquifers, we also share some examples of how regional aquifers can be characterised for modelling purposes, e.g. using the pressure and production histories of proximate fields. Based on simulation studies performed, we share anomalous observations resulting from the incorporation of open boundaries that dynamic modelling engineers should be wary of, e.g. plume movements against reservoir dip due to lower pressures at the boundary and numerical convergence issues when the CO2 plume contacts the open boundary. In relation to these observations, this paper also touches on parameters that can be sensitised to adjust plume behaviour, e.g. grid extensions and transmissibility multipliers. Examples shown have been drawn from anonymised projects in the Asia Pacific region.